Oracle内部视图:X$BH

X$BH Fixed Table Buffer Cache Diagram
Column     Type Description
~~~~~~     ~~~~~ ~~~~~~~~~~~
ADDR        RAW(4) Hex address of the Buffer Header.
INDX        NUMBER Buffer Header number
BUF#        NUMBER
HLADDR      RAW(4) Hash Chain Latch Address
See . ADDR
LRU_FLAG    NUMBER     8.1+ LRU flag
KCBBHLDF   0x01     8.1  LRU Dump Flag used in debug print routine
KCBBHLMT   0x02     8.1  moved to tail of lru (for extended stats)
KCBBHLAL   0x04     8.1  on auxiliary list
KCBBHLHB   0x08     8.1  hot buffer - not in cold portion of lru
FLAG        NUMBER
KCBBHFBD   0x00001       buffer dirty
KCBBHFAM   0x00002  7.3  about to modify; try not to start io
KCBBHFAM   0x00002  8.0  about to modify; try not to start io
KCBBHNAC   0x00002  8.1  notify dbwr after change
KCBBHFMS   0x00004       modification started, no new writes
KCBBHFBL   0x00008       block logged
KCBBHFTD   0x00010       temporary data - no redo for changes
KCBBHFBW   0x00020       being written; can't modify
KCBBHFWW   0x00040       waiting for write to finish
KCBBHFCK   0x00080  7.3  checkpoint asap
0x00080  8.0  not used
KCBBHFMW   0x00080  8.1  multiple waiters when gc lock acquired
KCBBHFRR   0x00100       recovery reading, do not reuse, being read
KCBBHFUL   0x00200       unlink from lock element - make non-current
KCBBHFDG   0x00400       write block & stop using for lock down grade
KCBBHFCW   0x00800       write block for cross instance call
KCBBHFCR   0x01000       reading from disk into KCBBHCR buffer
KCBBHFGC   0x02000       has been gotten in current mode
KCBBHFST   0x04000       stale - unused CR buf made from current
0x08000  7.3  Not used.
KCBBHFDP   0x08000  8.0  deferred ping
KCBBHFDP   0x08000  8.1  deferred ping
KCBBHFDA   0x10000       Direct Access to buffer contents
KCBBHFHD   0x20000       Hash chain Dump used in debug print routine
KCBBHFIR   0x40000       Ignore Redo for instance recovery
KCBBHFSQ   0x80000       sequential scan only flag
KCBBHFNW  0x100000  7.3  Set to indicate a buffer that is NEW
0x100000  8.0  Not used
KCBBHFBP  0x100000  8.1  Indicates that buffer was prefetched
KCBBHFRW  0x200000  7.3  re-write if being written (sort)
0x200000  8.0  Not used
KCBBHFFW  0x200000  8.1  Buffer has been written once
KCBBHFFB  0x400000       buffer is "logically" flushed
KCBBHFRS  0x800000       ReSilvered already - do not redirty
KCBBHFKW 0x1000000  7.3  ckpt writing flag to avoid rescan */
0x1000000  8.0  Not used
KCBBHDRC 0x1000000  8.1  buffer is nocache
0x2000000  7.3  Not used
KCBBHFRG 0x2000000  8.0  Redo Generated since block read
KCBBHFRG 0x2000000  8.1  Redo Generated since block read
KCBBHFWS 0x10000000 8.0  Skipped write for checkpoint.
KCBBHFDB 0x20000000 8.1  buffer is directly from a foreign DB
KCBBHFAW 0x40000000 8.0  Flush after writing
KCBBHFAW 0x40000000 8.1  Flush after writing
TS#         NUMBER 8.X Tablespace number
DBARFIL     NUMBER 8.X Relative file number of block
DBAFIL      NUMBER 7.3 File number of block
DBABLK      NUMBER Block number of block
CLASS       NUMBER See Note 33434.1
1,'data block',
2,'sort block',
3,'save undo block',
4,'segment header',
5,'save undo header',
6,'free list',
7,'extent map',
8,'1st level bmb',
9,'2nd level bmb',
10,'3rd level bmb',
11,'bitmap block',
12,'bitmap index block',
13,'file header block',
14,'unused',
15,'system undo header',
16,'system undo block',
17,'undo header',
18,'undo block'                -- since 10g
STATE       NUMBER
KCBBHFREE         0       buffer free
KCBBHEXLCUR       1       buffer current (and if DFS locked X)
KCBBHSHRCUR       2       buffer current (and if DFS locked S)
KCBBHCR           3       buffer consistant read
KCBBHREADING      4       Being read
KCBBHMRECOVERY    5       media recovery (current & special)
KCBBHIRECOVERY    6       Instance recovery (somewhat special)
MODE_HELD   NUMBER    Mode buffer held in (MODE pre 7.3)
0=KCBMNULL, KCBMSHARE, KCBMEXCL
CHANGES     NUMBER
CSTATE      NUMBER
X_TO_NULL   NUMBER Count of PINGS out (OPS)
DIRTY_QUEUE NUMBER You wont normally see buffers on the LRUW
LE_ADDR     RAW(4) Lock Element address (OPS)
SET_DS      RAW(4) Buffer cache set this buffer is under
OBJ         NUMBER       Data object number
TCH     NUMBER 8.1 Touch Count
TIM     NUMBER 8.1 Touch Time
BA          RAW(4)
CR_SCN_BAS  NUMBER       Consistent Read SCN base
CR_SCN_WRP  NUMBER       Consistent Read SCN wrap
CR_XID_USN  NUMBER CR XID Undo segment no
CR_XID_SLT  NUMBER CR XID slot
CR_XID_SQN  NUMBER CR XID Sequence
CR_UBA_FIL  NUMBER CR UBA file
CR_UBA_BLK  NUMBER CR UBA Block
CR_UBA_SEQ  NUMBER CR UBA sequence
CR_UBA_REC  NUMBER CR UBA record
CR_SFL      NUMBER
LRBA_SEQ    NUMBER } Lowest RBA needed to recover block in cache
LRBA_BNO    NUMBER }
LRBA_BOF    NUMBER }
HRBA_SEQ    NUMBER } Redo RBA to be flushed BEFORE this block
HRBA_BNO    NUMBER } can be written out
HRBA_BOF    NUMBER       }
RRBA_SEQ    NUMBER } Block recovery RBA
RRBA_BNO    NUMBER }
RRBA_BOF    NUMBER }
NXT_HASH    NUMBER Next buffer on this hash chain
PRV_HASH    NUMBER Previous buffer on this hash chain
NXT_LRU     NUMBER Next buffer on the LRU
PRV_LRU     NUMBER Previous buffer on the LRU
US_NXT      RAW(4)
US_PRV      RAW(4)
WA_NXT      RAW(4)
WA_PRV      RAW(4)
ACC         RAW(4)
MOD         RAW(4)

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